An electroencephalogram (EEG) is a test to detect problems in the electrical activity of the brain.

It is a physiological test, which is methodologically similar to EKG, different from imaging (CT, MRI, x-ray) or tissue sampling (blood, biopsy).

How the Test is Performed

Brain cells communicate with each other by producing tiny electrical impulses. In an EEG, this faint electrical activity is measured by putting electrodes on the scalp.The test is performed in your neurologist's office, at a hospital, or at an independent laboratory.

You will be asked to lie on your back on a bed (or in a reclining chair). The technician will apply between 16 and 21 flat metal disks(electrodes) in different positions on your scalp. The disks are held in place with a sticky paste inside a cap that will fit over the scalp. The electrodes are connected by wires to an amplifier and a recording machine. Needle electrodes are not used in our office.

The recording machine converts the electrical impulses into patterns that can be seen on a computer screen, as well as stored on a computer disk. Before computers, the activity was printed on paper.

The electical activity looks like a series of continuous wavy lines. You will need to lie completely still with your eyes closed because any movement can alter the results.You may be asked to do certain things during the recording, such as breathe deeply and rapidly for several minutes or look at a bright flashing light.

The activtiy occurs at different frequencies that all can be normal in certain situations. "Frequency" is the number of waves per second. Frequencies are different during wakefulnes, drowsiness and sleep. There are differents types of sleep associated with different waveforms. Certain medications can induce changes in the rhythms.

Brain waves are faster when you are awake, and, usually, slower when you're sleeping. There are also normal patterns to these waves. These frequencies and patterns are what the EEG reader is looking for.

How to Prepare for the Test

1. On the test day wash your hair thoroughly and dry, but please use NOTHING in your hair. (No hair spray, oils, or leave-in conditioner.)

2. Take all your medications as directed (unless otherwise instructed).

5. Good news: this test is painless. Although having electrodes pasted onto your skin may feel strange, they only record activity and do not produce any sensation. No significant electricity passes from the electrode into your skin. You will have no after-effects and you will be able to resume all your normal activities.

6. Eat before being tested: Two hours before the EEG, eat a regular meal (or at least a snack) to help stabilize blood sugar level. Do notdrink alcohol within 8 hours of the test.

Typical setup for EEG recording is shown in the picture below (this is not the office of Dr. Rosenkilde).

How To Prepare For a Sleep-Deprived EEG

Sometimes it is necessary to sleep during the test, so you may be asked to reduce your sleep the night before testing. If you're asked to have such a test, do not consume any caffeine, energy drinks, or other products that help you stay awake.

If your physician has requested a sleep EEG following overnight sleep deprivation, please follow these important guidelines:

1. Follow all directions in the section above. In addition:

2. You, (the patient) should remain awake the entire night.

4. The patient must remain awake on the way to the office and until the physician or EEG technician completes the hookup. If the patient falls asleep before the EEG, then he or she may not be able to sleep during the recording.

5. Arrangements should be made for transportation to and from the test.

Why an EEG is Performed

EEG is used to help diagnose if you're having seizures and if so, what type. Thus, it is commonly used to investigate any episode of unconsciousness or confusion. Head injury, stupor and coma can be associated with abnormalities. Epilepsy, seizures, convulsions, syncope, transient global amnesia, transient ischemic attack, stroke, brain tumor, disorientation, cerebral infections, encephalopathy are some of the diagnoses that a doctor may consider when an EEG is requested. Assessment of certain psychiatric conditions or suspicion of abnormal brain chemistry may involve EEG.

It is also used to:

Evaluate problems with sleep ( sleep disorders)

Monitor the brain during brain surgery

In extreme cases, the EEG may be done to show that the brain has no activity, in the case of someone in a deep coma. It can be helpful when trying to decide if someone is brain dead. EEG cannot be used to measure intelligence.

Significance of Abnormal Results Mean

Abnormal results on an EEG test may be due to:

An abnormal structure in the brain (such as a brain tumor)

Attention problems

Tissue death due to a blockage in blood flow (cerebral infarction)

Drug or alcohol abuse

Head injury

Inflammation of the brain (encephalitis)

Hemorrhage (abnormal bleeding caused by a ruptured blood vessel)

Migraines (in some cases)

Seizure disorder (such as epilepsy or convulsions)

Sleep disorder (such as narcolepsy)

Note: A normal EEG does not mean that a seizure did not occur.

Risks: The procedure is very safe. However, the flashing lights, fast breathing (hyperventilation), or sleep deprivation infrequently may trigger a seizure in those with seizure disorders.

It may be difficult to get the paste out of your hair, but it should come out after a few washings with regular shampoo.